mapOfMaps is package{
  MM has type ref hash of (string, ref hash of (string,integer));
  var MM := hash{};
  
  main() do {
    MM["a"] := _cell(hash{"b"->0});
    MM["b"] := _cell(hash{})
    
    -- (!MM["a"])["b"] := 1;
    M is MM["a"];
    M["b"] := 1;
    
    assert (!MM["a"])["b"]=1;
    
    N is MM["b"];
    N["c"] := 1;
    -- (!MM["b"])["c"] := 1;
    
    assert (!MM["b"])["c"]=1;
  }
}